1. Technical Field
The present disclosure relates to an epitaxial structure and a method for making the same.
2. Description of Related Art
Light emitting devices such as light emitting diodes (LEDs) using group III-V nitride semiconductors, such as gallium nitride (GaN), have been put into practice.
Since wide GaN substrate cannot be produced, the LEDs have been produced upon a heteroepitaxial substrate such as sapphire. The use of sapphire substrate is problematic due to lattice mismatch and thermal expansion mismatch between GaN and the sapphire substrate. One consequence of thermal expansion mismatch is bowing of the GaN/sapphire substrate structure, which leads in turn to cracking and difficulty in fabricating devices with small feature sizes. A method for solving the problem is forming a plurality of grooves on surface of the sapphire substrate by lithography or etching. However, the process of lithography and etching are complex, high cost, and may pollute the sapphire substrate.
What is needed, therefore, is to provide an epitaxial method for solving the problem discussed above.